Xbox is the embodiment or cautionary tale of what happens when suits take over from passionate knowledgable people.
The first half of the 360 lifespan back when they had all of the OG Xbox veterans and Peter Moore was incredible. They were hungry, they mostly understood the market and they really tried to innovate with the online play. They courted Japan as much as humanly possible which definitely paid dividends for the worldwide audience (pity Japan still ignored them but what can you do..).
Being first to the market was a brilliant strategic move despite the RRoD that their rushing caused. They caught Sony with their pants down, while at the same time Sony were arrogant and assumed they would simply inherit the PS2 market on brand name alone.
But then the suits slowly but surely pushed out all of the gaming people, all of the people who made the Xbox brand and the Xbox360 into a roaring success. I don't know all of the internal MS politics that goes on behind the scenes but you can see the terrible MBA tier decisions made by money men with no idea how the gaming market worked or why their console was successful.
You had the trippling down on Kinect which nobody asked for and released pretty much after the Wii fad had died down with the mainstream. They let Bungie go and bought Gears instead of just contracting Epic for exclusivity and then they tried to just factory line release Forza, Halo and Gears with no creative love or passion behind the projects, just "we need our X brand to release by Y timeframe, this will sell well and make our line on a graph go up!"
They stopped trying to court Japanese developers or fund exclusives and their first party output cratered into souless yearly "big 3" releases mostly by people not involved with the IP before and without the talent of the original developers (Halo, Gears). This pretty much killed both Halo and Gears franchises.
I mean say what you will about Gears and maybe the gameplay being stale or the multiplayer too insular for the mainstream, but motherfucking Halo was one of the biggest gaming franchises on Earth and their treatment of it was abysmal.
Then that is not even touching on the horrendous Xbox One debacle. They clown suits with no idea how to run a gaming company decided they would quadruple down on Kinect and force include it with every console as if that was something gamers actually wanted and wanted to turn the console into a fancy DVR/Media center, not to mention the always online DRM stuff and the fact that they wasted money on all of that shit while Sony just added better specs to their console leaving Xbox One lagging behind and losing the hardcore gamer.
I mean honestly, given how badly Sony fucked up the first half of the PS3's life and how well Xbox360 was handled for the first part of its life that generation/hardcore+mainstream audience momentum was theirs to lose. They should have knocked it out of the park and set up the next Xbox as a huge success. But already prior to Xbox One failure we saw exclusive titles, Japanese games and first party all kind of dry up in the tail end of the 360's life, while Sony were working hard to court gamers back to their PS3.
The tail end 360 failures plus the Xbox One blunder really meant that MS lost their audience and it looks like they never really recovered it. With current consoles we just see the continuation of this trend while clueless MS suits and execs still don't understand the market.
"Why don't we uhh... make the Netflix of gaming and release it on PC as well! That is sure to improve our brand and console sales! Plus it helps our datacenter revenue as we become our own customer!"
"Why don't we just buy up all of the biggest publishers? Gamers will HAVE to like us then! Plus we have a large content stream for our Netflix of gaming! Who cares if we pay 3 times the company's actual value!",
"Why don't we just release our own games on other consoles because....uh...something something profit??"
TL

R - Souless MBA money men suits took over and kicked out the people who made the Xbox 360 a success and understood the market. Since then they have blundered their way towards the path of irrelevance.